The development of vehicle propulsion using gaseous or liquefied fuels under pressure has led to a search for fuel storage techniques that make the following possible under the best possible safety conditions:                obtaining as high as possible an index of volume performance or filling coefficient (ratio of on-board volume to authorized size);        obtaining as high as possible a construction index (ratio of on-board volume to tank mass); and        using low cost technologies.        
With a liquefied petroleum gas (LPG) engine, service pressures are relatively low (about 1 MPa), so the construction index is less discriminating than the other factors.
In contrast, with a VNG engine, pressure is much higher, about 20 MPa. In this field, existing tanks are made up of one or more individual containers or modules of generally cylindrical shape made either of metal or of composite material.
A tank enabling fluid to be stored under high pressure while maintaining a good filling coefficient is proposed in patent application WO 98/26209. That prior art tank is made up of a plurality of individual tubular containers and presents polymorphic architecture with the following particular advantages:                it is very easy to adapt to the available space;        it is modular;        its storage volume is subdivided and it is possible, where necessary, to isolate individual containers in order to satisfy safety objectives; and        its mass is relatively low since the wall thickness requirement for each individual container is much less than that which would apply to a single-bodied tank with the same total working volume.        
When the modules are made of metal, they present a construction index that is relatively low. For modules made of composite material, the construction index is considerably higher, however the constraints concerning ability to withstand pressure lead to greater wall thickness, thereby affecting the filling coefficient. In addition, making monolithic tanks of the bottom+ferrule type out of composite material leads to significant manufacturing constraints, in particular for implementing the winding and/or draping of the fiber reinforcement of the composite material, and also for the necessary tooling, in particular mandrels or formers which must enable the wound or draped structure to be removed.
Patent application DE 3 026 116 proposes making a pressurized fluid tank comprising a plurality of tank portions in mutual contact via plane walls. The tank portions are held together by peripheral straps. Covers close the tank portions at their longitudinal ends. Longitudinal straps bear on the adjacent edges of the covers and contribute to holding them in place.
The fact that each cover is held by a single longitudinal strap which bears on a portion of the edge of the cover does not guarantee an ability to withstand high pressures.
In addition, the fact that each longitudinal strap is shared between two tank portions limits flexibility in tank construction, and in particular it does not enable tank portions of different lengths to be assembled together.
An improvement in the ability of tanks to withstand pressure by using straps is also described in document JP 10-274391 which shows the use of peripheral straps in the form of fiber-reinforced tapes.